Using full-term, newborn beagle puppies as subjects, to determine the effect of prostaglandins on the retinal vessels of the immature eye. In particular, the possiblity that high arterial oxygen tension might result in prostaglandin mediated retinal vasoconstriction following change in the tissue concentration level of either constrictor or dilator prostaglandins will be investigated. The possibility that indamethicin (used to prevent premature labor during pregnancy) might cross the placenta and inhibit prostaglandin formation thus making the retinal vessels more or less susceptible to oxygen vasoconstriction will also be investigated. These studies will be performed using the new method of indocyanine green dye angiography which for the first time permits visualization of the immature retinal vasculatue without surgical intervention. Endogenous prostaglandins E and F will be measured by specific radioimmunoassay; radiolabeled prostaglandins will be used to define diffusion characteristics of injected prostaglandins. Indomethacin levels will be determined by gas chromatography. Damage to retinal endothelium will be assessed microscopically and with fluorescein dye angiography. Results from these studies could provide an understanding of mechanisms of blood flow control in retina vasculature and a rational basis for treatment and prevention of retrolental fibroplasia (RLF).